Light-emitting device

ABSTRACT

A light-emitting device comprising a semiconductor light-emitting stack, comprising a light emitting area; an electrode formed on the semiconductor light-emitting stack, wherein the electrode comprises a current injected portion and an extension portion; a current blocking structure formed between the current injected portion and the semiconductor light-emitting stack, and formed between a first part of the extension portion and the semiconductor light-emitting stack; and an electrical contact structure formed between a second part of the extension portion and the semiconductor light-emitting stack.

BACKGROUND OF THE DISCLOSURE

1. Technical Field

The present invention relates to a light-emitting device, and inparticular to a semiconductor light-emitting device.

2. Description of the Related Art

The light-emitting mechanism and the structure of a light-emitting diode(LED) are different from that of the conventional light sources. The LEDhas advantages of small size and high reliability, and been widely usedin different fields such as displays, laser diodes, traffic lights, datastorage apparatus, communication apparatus, lighting apparatus, andmedical apparatus. Because of the successful development of highbrightness LEDs, LED can be applied to indoor or large outdoor displays.How to improve the light emitting efficiency of light emitting devicesis an important issue in this art.

SUMMARY OF THE DISCLOSURE

Accordingly, the present invention provides a light-emitting device. Thelight-emitting device includes a semiconductor light-emitting stackhaving a light emitting area; an electrode formed on the semiconductorlight-emitting stack, wherein the electrode comprises a current injectedportion and an extension portion; a current blocking area formed betweenthe current injected portion and the semiconductor light-emitting stack,and formed between a first part of the extension portion and thesemiconductor light-emitting stack; and an electrical contact structureformed between a second part of the extension portion and thesemiconductor light-emitting stack, wherein the first part of theextension portion is closer to current injected portion than the secondpart of the extension portion is, and wherein the ratio of theelectrical contact structure and the light emitting area is between 3%to 15%.

Further scope of the applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide easy understanding ofthe invention, and are incorporated herein and constitute a part of thisspecification. The drawings illustrate embodiments of the invention and,together with the description, serve to illustrate the principles of theinvention.

FIG. 1A is a cross-sectional view of a light-emitting device inaccordance with a first embodiment of the present invention.

FIG. 1B is a top view of a light-emitting device in accordance with thefirst embodiment of the present invention.

FIG. 1C is a top view of a conventional light-emitting device.

FIG. 2A is a cross-sectional view of a light-emitting device inaccordance with a second embodiment of the present invention.

FIG. 2B is a top view of a light-emitting device in accordance with thesecond embodiment of the present invention.

FIG. 3A is a cross-sectional view of a light-emitting device inaccordance with a third embodiment of the present invention.

FIG. 3B is a top view of a light-emitting device in accordance with thethird embodiment of the present invention.

FIG. 4A is a cross-sectional view of a light-emitting device inaccordance with a fourth embodiment of the present invention.

FIG. 4B is a top view of a light-emitting device in accordance with thefourth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers are used in thedrawings and the description to refer to the same or like parts.

Referring to FIGS. 1A-1B, the cross-sectional views show alight-emitting device 1 in accordance with a first embodiment of thepresent invention. The light-emitting device 1 such as an LED comprisesa substrate 100, a semiconductor light-emitting stack 110, an electricalcontact structure 140, a first electrode 120, and a second electrode130. The material of the substrate 100 includes semiconductor materialssuch as Si, SiC, GaAsP, GaAs, or GaP. The semiconductor light-emittingstack 110 formed on the upper surface of the substrate 100 includes ann-type semiconductor layer 112, a p-type semiconductor layer 114, and anactive layer 113 interposed therebetween. In some embodiments, thearrangements of the n-type and p-type semiconductor layers 112 and 114can be interchanged. In the embodiment, the n-type and p-typesemiconductor layers 112 and 114 act as cladding layers of the LED andinclude III-V group compound semiconductor materials such as AlGaInP,AlGaAs, AlGaInN, or other ternary or quaternary III-V group compoundsemiconductor materials. The active layer 113 acts as a light-emittinglayer including III-V group compound semiconductor materials such asAlGaInP, AlGaInN or other materials matched with the n-type and p-typesemiconductor layers 112 and 114. The first electrode 120 and the secondelectrode 130 are formed on the bottom of the substrate 100 and the topof the semiconductor light-emitting stack 110 respectively. In theembodiment, the second electrode 130 includes a current injected portion131 and extension portion 132. In the embodiment, the current injectedportion 131 is deposited approximately on the center of the p-typesemiconductor layers 114. The extension portions 132 comprise firstbranches 1321 radiate from the current injected portion 131 toward theedges of the light-emitting device 1. Second branches 1322 are divergingand extending from the first branches. The second branches are depositedalong with and paralleled to the edges of the light-emitting device 1.The electrical contact structure 140 is formed between the secondbranches and the semiconductor light-emitting stack 110. A method offorming the electrical contact structure 140 includes forming asemiconductor layer on the semiconductor light-emitting stack 110, whichis ohmically contacted with the extension portions 132. Then etching thesemiconductor layer in accordance with a predetermined pattern. Afterthat, part of the p-type semiconductor layer 114 is exposed, and theremaining region of the semiconductor layer forms the electrical contactstructure 140. Afterwards, the electrodes are formed on the p-typesemiconductor layer 114 and the electrical contact structure 140.

Another method for forming the electrical contact structure 140 includesa step of forming an insulated layer on the semiconductor layer to coverthe area with another predetermined pattern. The exposed region of thesemiconductor layer is the electrical contact structure.

The conductive type of the electrical contact structure 140 can be thesame as the p-type semiconductor layer 114 or different from it. If theconductivity of the electrical contact structure 140 is n-type, it alsoforms a reverse tunneling contact with the p-type semiconductor layer114. Another material of the electrical contact structure 140 is metalwhich can be partially deposited on the p-type semiconductor layer 114with a predetermined pattern to form the electrical contact structure140.

In one embodiment, the material of the electrical contact structure 140is a p-type semiconductor. The second branches 1322 are electricallycontacted with the electrical contact structure 140. Because the firstbranches 1321 and the current injected portion 131 are current-blockedwith the p-type semiconductor layer 114, the current is injected throughthe current injected portion 131, moves to the first branches 1321 andthe second branches 1322, and then is spread to the semiconductorlight-emitting stack 110 through the electrical contact structure 140.In the embodiment, the size of the light-emitting device 1 is 10 mil×10mil, and the area of the active layer 113 is 67.24 mil². The width ofeach of the first branches 1321 is 0.2 mil, and the width of each of thesecond branches 1322 is 0.4 mil. The width of each of the electricalcontact structure 140 is 0.3 mil. The electrical contact structure 140and the second branches 1322 c have substantially the same shape. Thetotal area of the extension portions 132 is 11.64 mil² and the totalarea of the electrical contact structure 140 is 5.8 mil². The area ratioof the electrical contact structure 140 and the active layer 113 is8.62%. The luminous efficiency of the light-emitting device 1 is 47.62μm/W. When the width of the second branch 1322 is varied from 0.4 mil to0.45 mil and the width of the electrical contact structure 140 is variedfrom 0.3 mil to 0.35 mil, the area ratio of the electrical contactstructure 140 and the active layer 113 is 10.18% and the luminousefficiency of the light-emitting device 1 is 46.48 lm/W. When the widthof each second branch 1322 is varied to 0.5 mil, and the width of theelectrical contact structure 140 is varied to 0.4 mil, the area ratio ofthe electrical contact structure 140 and the active layer 113 is 11.77%and the luminous efficiency of the light-emitting device 1 is 46.13lm/W.

FIG. 1C shows the top view of a conventional light-emitting devicewithout implementing the present invention. The electrical contactstructure 140 is formed under the first branches 1321 and the secondbranches 1322. The luminous efficiency of the light-emitting device 1 is46.01 lm/W which is lower than that of the light-emitting device 1 inaccordance of the first embodiment of the present invention.

In some embodiments, the surface of the semiconductor light-emittingstack 110 and/or the interface between the semiconductor light-emittingstack 110 and the substrate 100 can be optionally roughened to improvethe light extraction efficiency. The roughened surface can be formedduring the epitaxial process, by a randomly etching method or alithographical etching to form a regular or an irregular patternedsurface.

FIGS. 2A-2B show the cross-sectional views of a light-emitting device 2in accordance with a second embodiment of the present invention. Thelight-emitting device 2 includes a substrate 200, a conductive adhesivelayer 201, a reflective layer 202, a first transparent conductive oxidelayer 220, a semiconductor light-emitting stack 210, an electricalcontact structure 250, a first electrode 230, and a second electrode240.

The material of the substrate 200 includes but is not limited to Si,GaAs, metal or other similar materials which can mechanically supportthe other structure of the light-emitting device 2. The conductiveadhesive layer 201 is formed on the substrate 200, and a first bondinginterface is formed therebetween. The material of the conductiveadhesive layer 201 includes but is not limited to Ag, Au, Al, In,spontaneous conductive polymer, or polymer doped with conductivematerials like Al, Au, Pt, Zn, Ag, Ni, Ge, In, Sn, Ti, Pb, Cu, Pd, orother metals. The reflective layer 202 is formed on the conductiveadhesive layer 201, and a second bonding interface is formedtherebetween. The material of the reflective layer 202 includes but isnot limited to metal, insulated material, or the combination thereof.The metal material for the reflective layer 202 includes Al, Au, Pt, Zn,Ag, Ni, Ge, In, Sn or alloys of the abovementioned metals. The insulatedmaterial for the reflective layer 202 includes but is not limited toAlO_(x), SiO_(x), or SiN_(x). The first transparent conductive oxidelayer 220 formed on the reflective layer 202 includes materials such asindium tin oxide, cadmium tin oxide, zinc oxide, or zinc tin oxide.

The semiconductor light-emitting stack 210 formed on the firsttransparent conductive oxide layer 220 includes a thick semiconductorlayer 211, a p-type semiconductor layer 214, an n-type semiconductorlayer 212, and an active layer 213 interposed therebetween. In theembodiment, the semiconductor light-emitting stack 210 is etchedpartially from the n-type semiconductor layer 212, the active layer 213,and the p-type semiconductor layer 214 to the thick semiconductor layer211 to expose part of the thick semiconductor layer 211. The materialsof the n-type and p-type semiconductor layers 212 and 214 include III-Vgroup compound semiconductor materials such as AlGaInP, AlGaAs, AlGaInNor other ternary or quaternary III-V group compound semiconductormaterials. The active layer 213 includes III-V group compoundsemiconductor materials such as AlGaInP, AlGaInN or other materialsmatched with the n-type and p-type semiconductor layers 212 and 214. Thethick semiconductor layers 211 acts as a light extraction layer forimproving the light extraction efficiency and includes materials such asGaP or GaN.

The method of forming the light-emitting device 2 includes forming asemiconductor layer on a growth substrate (not illustrated), and nextforming the semiconductor light-emitting stack 210 on the semiconductorlayer. After the semiconductor light-emitting stack 210 is grown, thefirst transparent conductive oxide layer 220 is formed on thesemiconductor light-emitting stack 210, which can spread the currentinjected from the electrode. Next, the reflective layer 202 is formed onthe first transparent conductive oxide layer 220. Then, thesemiconductor light-emitting stack 210 with the first transparentconductive oxide layer 220 and the reflective layer 202, and thesubstrate 200 are adhered together by the adhesive layer 201.

After the adhering step, the growth substrate is removed, and thesemiconductor layer is etched with a predetermined pattern. Part of then-type semiconductor layer 212 is exposed, and the remainingsemiconductor layer forms the electrical contact structure 250.

The first and second electrodes 230 and 240 are formed on the topsurface of the semiconductor light-emitting stack 210 and the bottom ofthe substrate 200 respectively. In the embodiment, the second electrode240 includes a current injected portion 241 and extension portions 242.In the embodiment, the current injected portion 241 is depositedapproximately on the center of the semiconductor light-emitting stack210. The extension portions 242 comprise first branches 2421 radiatingfrom the current injected portion 241 toward the edges of thelight-emitting device 2. Second branches 2422, third branches 2423, andfourth branches 2424 are diverging and extending from the first branchesrespectively. The second branches 2422 are deposited along with andparallel to the edges of the light-emitting device 2. The second, thirdand fourth branches 2422, 2423, 2424 are parallel to each other. Theelectrical contact structure 250 is formed between the second, third andfourth branches 2422, 2423, 2424 and the semiconductor light-emittingstack 210 respectively. In this embodiment, the material of theelectrical contact structure 250 is an n-type semiconductor includingIII-V group compound semiconductor materials such as GaP, GaAs, GaN orother ternary or quaternary III-V group compound semiconductormaterials. The second, third and fourth branches 2422, 2423, 2424 areelectrical contact with the electrical contact structure 250. The firstbranches 2421 and the current injected portion 241 are current-blockedwith the semiconductor light-emitting stack 210. The current is injectedthrough the current injected portion 241 and moves to the first, second,third and fourth branches 2421, 2422, 2423, 2424, and then is spread tothe semiconductor light-emitting stack 210 through the electricalcontact structure 250. In the embodiment, the size of the light-emittingdevice 2 is 28 mil×28 ml, and the area of the active layer 213 is 645.16mil². The width of each of the first branches 2421 is 0.15 mil. Thewidth of each of the second, third and fourth branches 2422, 2423, 2424is 0.4 mil. The width of each of the electrical contact structure 250 is0.3 mil. The electrical contact structure 250 and the second brancheshave substantially the same shape. The total area of the extensionportions 242 is 34.39 mil², and the total area of the contact structure250 is 41.16 mil². The area ratio of the electrical contact structure250 and the active layer 213 is 6.38%. The luminous efficiency of thelight-emitting device 2 is 55 m/W.

In another embodiment, a structure of a light-emitting device withoutthe conductive adhesive layer 201 and the first transparent conductiveoxide layer 220 can be formed by direct bonding method with highpressure to join the semiconductor light-emitting stack 210 and thesubstrate 200, or join the reflective layer 202 and the substrate 200together.

In another embodiment, a second transparent conductive oxide layer canbe formed on the semiconductor light-emitting stack 210, and includesmaterials such as indium tin oxide, cadmium tin oxide, zinc oxide, orzinc tin oxide.

FIGS. 3A-3B show the cross-sectional views of a light-emitting device 3in accordance with a third embodiment of the present invention. Thestructure of the light-emitting device 3 is similar to the lightemitting device 1, and the difference is the n-type semiconductor 212 ofthe light emitting device 3 includes a roughened top surface. Theroughened top surface can be formed during the epitaxial process or by arandomly etching method to form a multi-cavity surface. It also can beformed by a lithographical etching to form a regular or an irregularpatterned surface. The n-type semiconductor 212 also includes an eventop surface. A second electrode 340 is formed on the even top surface.The second electrode 340 includes a current injected portion 341 andwindmill-like extension portions 342. In the embodiment, the currentinjected portion 341 is deposited approximately on the center of theeven top surface of the n-type semiconductor layer 212. Thewindmill-like extension portions 342 comprise branches 3421 radiatingfrom the current injected portion 341 and form a windmill like shape.The branches 3421 comprise first regions and second regions, wherein thefirst regions are closer to the current injected portion 341 than thesecond regions are. There is an electrical contact structure 350 formedbetween second regions of branches 3421 and the semiconductorlight-emitting stack 210, and the electrical contact structure 350 areohmically contacted with the second regions of branches 3421. In thisembodiment, the material of the electrical contact structure 350 is ann-type semiconductor including III-V group compound semiconductormaterials such as GaP, GaAs, GaN or other ternary or quaternary III-Vgroup compound semiconductor materials. The first regions of branches3421 and the current injected portion 341 are current-blocked with thesemiconductor light-emitting stack 210. The current is injected throughthe current injected portion 341 and moves to the branches 3421, andthen is spread to the semiconductor light-emitting stack 210 through theelectrical contact structure 350. In the embodiment, the size of thelight-emitting device 3 is 14 mil×14 mil, and the area of the activelayer 213 is 135 mil². The width of each of the branches 3421 is 0.25mil. The width of each of the electrical contact structure 350 is 0.15mil. The electrical contact structure 350 and the second regions ofbranches have substantially the same shape. The total area of theextension portions 342 is 8.13 mil², and the total area of theelectrical contact structure 350 is 3.37 mil². The area ratio of theelectrical contact structure 350 and the active layer 213 is 2.51%. Theluminous efficiency of the light-emitting device 3 is 67 μm/W.

In a conventional light-emitting device, the electrical contactstructure 350 is varied to be formed between the first and secondregions of the extension portions 342 and the semiconductorlight-emitting stack 210, the total area of the electrical contactstructure 350 is 4.89 mil². The area ratio of the electrical contactstructure 350 and the active layer 213 is 3.64%. The luminous efficiencyof the conventional light-emitting device is 65 μm/W which is lower thanthat of the light-emitting device 3 in accordance with the thirdembodiment of the present invention.

FIGS. 4A-4B show the cross-sectional view of a light-emitting device 4in accordance with a fourth embodiment of the present invention. Thelight-emitting device 4 includes a substrate 400, a conductive adhesivelayer 401, a reflective layer 402, a first transparent conductive oxidelayer 420, a semiconductor light-emitting stack 410, a current blockingstructure 403 formed between the first transparent conductive oxidelayer 420 and the semiconductor light-emitting stack 410, an electricalcontact structure 450, a first electrode 430, and a second electrode440. The material of the substrate 400 includes but is not limited toSi, GaAs, metal or other similar materials which can mechanicallysupport the other structure of the light-emitting device 4. Theconductive adhesive layer 401 is formed on the substrate 400, and afirst bonding interface is formed therebetween. The material of theconductive adhesive layer 401 includes but is not limited to Ag, Au, Al,In, spontaneous conductive polymer, or polymer doped with conductivematerials like Al, Au, Pt, Zn, Ag, Ni, Ge, In, Sn, Ti, Pb, Cu, Pd, orother metals. The reflective layer 402 is formed on the conductiveadhesive layer 401, and a second bonding interface is formedtherebetween. The material of the reflective layer 402 includes but isnot limited to metal, oxide, or the combination thereof. The metalmaterial for the reflective layer 402 includes Al, Au, Pt, Zn, Ag, Ni,Ge, In, Sn or alloys of the abovementioned metals. The first transparentconductive oxide layer 420 is formed on the reflective layer 402, andincludes but is not limited to indium tin oxide, cadmium tin oxide, zincoxide, or zinc tin oxide. The material of current blocking structure 403includes but is not limited to AlO_(x), SiO_(x), SiN_(x), or metal. Themetal of the current blocking structure 403 is selected from materialcapable of forming a Schottky contact with the first transparentconductive oxide layer 420. The semiconductor light-emitting stack 410is formed on the first transparent conductive oxide layer 420, includinga thick semiconductor layer 411, a p-type semiconductor layer 414, ann-type semiconductor layer 412, and an active layer 413 interposedtherebetween. In the embodiment, the semiconductor light-emitting stack410 is etched partially from the n-type semiconductor layer 412, theactive layer 413, and the p-type semiconductor layer 414 to the thicksemiconductor layer 411 to expose part of the thick semiconductor layer411. The n-type semiconductor 412 of the light emitting device 4includes a roughened top surface. The materials of the n-type and p-typesemiconductor layers 412 and 414 include III-V group compoundsemiconductor materials such as AlGaInP, AlGaAs, AlGaInN or otherternary or quaternary III-V group compound semiconductor materials. Theactive layer 413 includes III-V group compound semiconductor materialssuch as AlGaInP, AlGaInN or other materials matched with the n-type andp-type semiconductor layers 412 and 414. The thick semiconductor layers411 acts as a light extraction layer for improving the light extractionefficiency and includes materials such as GaP or GaN.

The method of forming the light-emitting device 4 includes forming asemiconductor layer on a growth substrate (not illustrated), forming thesemiconductor light-emitting stack 410 on the semiconductor layer,forming current blocking structure 403 on the semiconductorlight-emitting stack 410, forming the first transparent conductive oxidelayer 420 on the semiconductor light-emitting stack 410 and currentblocking structure 403 with a first predetermined pattern, and formingthe reflective layer 402 on the first transparent conductive oxide layer420 to form a first stack. Next the first stack and the substrate 400are adhered together by the adhesive layer 401.

After the adhering step, the growth substrate is removed, and thesemiconductor layer is etched in accordance with a second predeterminedpattern to expose part of the n-type semiconductor layer 412, and theremaining semiconductor layer forms the electrical contact structure450. In this embodiment, the material of the electrical contactstructure 450 is an n-type semiconductor including III-V group compoundsemiconductor materials such as GaP, GaAs, GaN or other ternary orquaternary III-V group compound semiconductor materials.

The first and second electrodes 430 and 440 are formed on the topsurface of the semiconductor light-emitting stack 410 and the electricalcontact structure 450, and the bottom of the substrate 400 respectively.In the embodiment, the second electrode 440 includes a current injectedportion 441 and extension portions 442. In the embodiment, the currentinjected portion 441 is deposited approximately on the center ofsemiconductor light-emitting stack 410. The extension portions 442comprise first branches 4421 radiating from the current injected portion441 toward the edges of the light-emitting device 4. Second branches4422 are diverging and extending from the first branches 4421. Thesecond branches 4422 are deposited along with and parallel to the edgesof the light-emitting device 4. The electrical contact structure 450 isformed between the second branches 4422 and the semiconductorlight-emitting stack 410. The second predetermined pattern of theelectrical contact structure 450 is similar to that of the secondbranches 4422. The second branches 4422 are electrically contacted withthe electrical contact structure 450. The first branches 4421 and thecurrent injected portion 441 are current-blocked with the semiconductorlight-emitting stack 410.

The current blocking structure 403 is deposited under the secondbranches 4422 and between the p-type semiconductor layer 414 and thefirst transparent conductive oxide layer 420. The first predeterminedpattern of the current blocking structure 403 is similar to that of theelectrical contact structure 450, and the width of the current blockingstructure 403 is larger than that of the electrical contact structure450 so the area of the current blocking structure 403 is larger thanthat of the electrical contact structure 450. The current is injectedthrough the current injected portion 441 and moves to the first andsecond branches 4421, 4422 and then is spread to the semiconductorlight-emitting stack 410 through the electrical contact structure 450.The current is blocked by the current blocking structure 403 so there isless light generated by the active layer under the second branches 4422and less light is absorbed by the second branches 4422.

In the embodiment, the size of the light-emitting device 4 is 14 mil×14mil, and the area of the active layer 413 is 135 mil². The width of eachof the first branches 4421 is 0.14 mil, and the width of each of thesecond branches 4422 is 0.24 mil. The width of each of the electricalcontact structure 450 is 0.14 mil, and the width of each of the currentblocking structure 403 is 0.12 mil.

The electrical contact structure 450 and the second branches havesubstantially the same shape. The total area of the extension portions442 is 8.83 mil², and the total area of the contact structure 450 is4.26 mil². The area ratio of the electrical contact structure 450 andthe active layer 413 is 3.16%. The luminous efficiency of thelight-emitting device 4 is 80 μm/W.

It will be apparent to a person having ordinary skill in the art thatvarious modifications and variations can be made to the structure of thepresent invention without departing from the scope or spirit of theinvention. In view of this, it is intended that the present inventioncovers modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A light-emitting device comprising: a semiconductor light-emittingstack, comprising a light emitting area; at least an electrode formed onthe semiconductor light-emitting stack, wherein the electrode comprisesa current injected portion and an extension portion wherein theextension portion having a first part and a second part; a first currentblocking structure formed between the current injected portion and thesemiconductor light-emitting stack, and formed between the first part ofthe extension portion and the semiconductor light-emitting stack; and anelectrical contact structure formed between the second part of theextension portion and the semiconductor light-emitting stack, whereinthe first part of the extension portion is closer to the currentinjected portion than the second part of the extension portion is, andwherein the ratio of the electric contact structure and the lightemitting area is between 3% to 15%.
 2. A light-emitting device accordingto claim 1, wherein the extension portion comprises a first branchradiating from the current injected portion and a second branchdiverging and extending from the first branches, wherein the second partis part of the second branch.
 3. A light-emitting device according toclaim 2, wherein the current injected portion is formed approximately onthe center of the semiconductor light-emitting stack, and the firstbranch radiates from the current injected portion toward the edge of thelight-emitting device.
 4. A light-emitting device according to claim 2,wherein the electrical contact structure and the second branches havesubstantially the same shape.
 5. A light-emitting device according toclaim 1, wherein the extension portion comprises first branchesradiating from the current injected portion into a windmill-like shape,at least one of the branches comprises the first part and the secondpart, and the electrical contact structure and the second part of thebranch have substantially the same shape.
 6. A light-emitting deviceaccording to claim 1, wherein the semiconductor light-emitting stackcomprising an n-type semiconductor layer, a p-type semiconductor layer,and an active layer interposed therebetween.
 7. A light-emitting deviceaccording to claim 1, further comprising a first transparent conductiveoxide layer formed between the semiconductor light-emitting stack andthe electrode.
 8. A light-emitting device according to claim 1, whereinthe semiconductor light-emitting stack comprising a roughened surface.9. A light-emitting device according to claim 8, wherein the roughenedsurface comprising a patterned surface or a multi-cavity surface.
 10. Alight-emitting device according to claim 1, further comprising asubstrate deposited on the semiconductor light-emitting stack.
 11. Alight-emitting device according to claim 10, further comprising aninterface formed between the semiconductor light-emitting stack and thesubstrate, wherein the interface is a roughened surface.
 12. Alight-emitting device according to claim 11, further comprising a firstbonding interface formed between the semiconductor light-emitting stackand the substrate.
 13. A light-emitting device according to claim 12,further comprising an adhesive layer formed between the semiconductorlight-emitting stack and the substrate, wherein the first bondinginterface is formed between the adhesive layer and the semiconductorlight-emitting stack, and a second bonding interface is formed betweenthe adhesive layer and the substrate.
 14. A light-emitting deviceaccording to claim 13, wherein the adhesive layer is a conductiveadhesive layer.
 15. A light-emitting device according to claim 14,wherein the conductive adhesive layer comprising at least one materialselected from the group consisting of Ag, Au, Al, In, Sn, AuSn alloy,spontaneous conductive polymer, and polymer doped with conductivematerials like Al, Au, Pt, Zn, Ag, Ni, Ge, In, Sn, Ti, Pb, Cu, or Pd.16. A light-emitting device according to claim 14, wherein the firstbonding interface and/or the second bonding interface comprises aroughened surface.
 17. A light-emitting device according to claim 14,further comprising a second current blocking structure between thesemiconductor light-emitting stack and the adhesive layer with apredetermined pattern.
 18. A light-emitting device according to claim17, further comprising a transparent conductive oxide layer between thesecond current blocking and the adhesive layer.
 19. A light-emittingdevice according to claim 17, wherein the second current blockingstructure is under the electrical contact structure.
 20. Alight-emitting device according to claim 17, wherein the predeterminedpattern is similar to the shape of the electrical contact structure. 21.A light-emitting device according to claim 17, wherein the area of thesecond current blocking structure is larger than the electrical contactstructure.
 22. A light-emitting device according to claim 17, whereinthe second current blocking structure comprising at least one materialselected from the group consisting of AlO_(x), SiO_(x), SiN_(x), andmetal.